Aiming at the problem that atmospheric laser communication is easily affected by atmospheric turbulence, which will lead to the degradation of communication quality, RNN and LSTM were established based on deep learning to predict refractive index structure constant, one of the most important parameters of atmospheric turbulence. Based on it, reference for the selection of atmospheric laser communication channels can be provided to avoid waste of channel resources. Three statistical values average absolute error, root mean square error and correlation coefficient were used to analyze the prediction results. The results showed that both RNN and LSTM can predict very well under medium and strong turbulence. The correlation coefficient between the predicted data and the original data were 67.37% and 96.17%.
Proc. SPIE. 11048, 17th International Conference on Optical Communications and Networks (ICOCN2018)
KEYWORDS: Visibility through fog, Signal attenuation, Air contamination, Telecommunications, Transmittance, Antennas, Atmospheric modeling, Systems modeling, Free space optical communications, Atmospheric optics
Considering the weather’s influence to atmospheric transmittance, the paper modifies the attenuation matrix in the basement of original MIMO FSOC system channel model. And then, based on the modified channel model, the capacity in different given conditions is shown through numerical simulation. The paper simulates the capacity in different transmitting antenna’s height as well as in different weather. Considering that in most conditions, the optical signal doesn’t transfer vertically, the paper stimulates the capacity versus system slant angle. The paper also simulates difference value of capacity. At last, the paper designs a software to evaluate whether the given conditions are fit for communication or not.
The application of asymmetrically clipped optical-orthogonal frequency division multiplexing (ACO-OFDM) in free-space optical (FSO) communication system can increase the system channel capacity, while the use of channel estimation technology can ensure that ACO-OFDM has better performance. Since the channel estimation performance is directly affected by the selection of pilot patterns, especially when using compressed sensing (CS), it has been a major task in OFDM transmission schemes. In order to improve the channel reconstruction accuracy, a hybrid optimization algorithm based on genetic algorithm (GA) and particle swarm optimization (PSO) algorithm is proposed for two types of pilot design criterion. Simulation results show that compared with other three algorithms, the proposed algorithm has faster convergence speed and lower convergence value. With the pilots designed by the proposed algorithm, the system can achieve higher channel reconstruction accuracy.
Beaconless spatial acquisition contribute a lot to designing a more integrated and smaller laser communication terminal for optical inter-satellite communication. In this paper, we present an analytical model of beaconless spatial acquisition on the influence of vibration. Two kinds of scan methods are analyzed, which are single scan and multi-scan. The analytical expressions of the acquisition probability of single scan and the mean acquisition time of multi-scan are derived. Numerical simulation and Monte Carlo experiment are adopted. The simulation results show that the acquisition probability of single scan asymptotically approaches a constant value with the increase of vibration levels and becomes higher if the beam divergence is increased, but the scan beam gain decrease at the same time. So, the overall acquisition link margin should be sufficient when increasing the beam divergence. What’s more, the accurate location of the target satellite has a great influence on the acquisition probability. When it comes to the multi-scan mode, the shortest mean acquisition time is got at the vibration level of 40μrad. And, the increase of multi-scan times can overcome the influence of vibration efficiently. The conclusions above can give some guides to the design of beaconless spatial acquisition system.
We present the performance benefits of differential phase-shift keying (DPSK) modulation in eliminating influence from atmospheric turbulence, especially for coherent free space optical (FSO) communication with a high communication rate. Analytic expression of detected signal is derived, based on which, homodyne detection efficiency is calculated to indicate the performance of wavefront compensation. Considered laser pulses always suffer from atmospheric scattering effect by clouds, intersymbol interference (ISI) in high-speed FSO communication link is analyzed. Correspondingly, the channel equalization method of a binormalized modified constant modulus algorithm based on set-membership filtering (SM-BNMCMA) is proposed to solve the ISI problem. Finally, through the comparison with existing channel equalization methods, its performance benefits of both ISI elimination and convergence speed are verified. The research findings have theoretical significance in a high-speed FSO communication system.